In automotive heating and air conditioning systems, the air flow through a heat exchanger core is induced by a blower upstream of the core and connected by a passage to the core. The radial flow squirrel cage type of blower is commonly used due to its efficiency and compactnes. Such blower, however, do produce an output which is nonuniform across the passage. This is illustrated in the prior art example of FIG. 1. There, a radial flow blower wheel 10 housed in a snail-shaped shroud 12 supplies air to the shroud opening 14. A ventilation case 16 containing a heat exchanger core 18 for either a heater or an air conditioner is connected to the shroud 12 at the opening 14 to define a divergent air passage 19 between the blower and the heat exchanger. The shroud 12 and case 16 together comprise a housing. Downstream of the core 18, the ventilation case 16 forms a duct 20.
The blower wheel 10 pulls air into the shroud 12. The amount of air moved by the blower increases as a point on the wheel moves within the shroud from the edge 22 of the opening. The shroud is positioned progressively further from the wheel in the direction of rotation to accommodate the growing volume of air. The blower action produces a stream 24 of high velocity air which is ejected from the shroud opening 14. The high velocity stream 24 tends to stay together, hugging the wall 26 of the case which is adjacent the edge 22. A relatively low velocity movement of air passes through the region between the stream 24 and the case wall 28 which is opposite the wall 26. That airflow pattern forces most of the air through a very small area of the core. In the case of a heater core, the coolant within the core is reduced to a low temperature in the small area and is thus limited in the rate of heat transfer so that the majority of the air is poorly heated. The coolant in the remainder of the core is cooled only slightly due to the low rate of air flow in that region, although that small amount of air is well heated. Thus the overall heat transfer rate is poor. Such operation also results in hot and cold air streams emerging from the core, and they are difficult to mix uniformly. A further effect of passing the majority of the air through a small area of the core is a very high pressure drop through the core.
It is desirable that the air velocity be somewhat uniform over the core area for optimum heat transfer, low pressure drop and uniform temperature. This has been accomplished in the past by providing a plenum between the blower and heat exchanger core to allow the air stream to settle before passing through the core. However, in some applications space constraints require that a heat exchanger be placed nearly perpendicular to the wall 26 of the case and so close to the shroud opening 14 that there is no room for a plenum.
U.S. Pat. No. 4,712,611 to Witzel discloses a blower and a heat exchanger with a profiled grid positioned in the flow of air from the blower to spread the air so that it substantially covers the heat exchanger area. According to Witzel, the flow in the absence of the grid is mainly in the center of the heat exchanger. The grid imposes a distributed flow resistance in the air path so that the air flow is deflected in accordance with the grid permeability and configuration to increase the flow at the edges of the heat exchanger.